This invention relates generally to variable clearance packing for rotatable machines and more particularly, to a method and apparatus for providing variable clearance packing utilizing retractable packing components for rotary machines such as steam and gas turbines.
Rotary machines such as steam and gas turbines used for power generation and mechanical drive applications are generally large machines consisting of multiple turbine stages. In such machines, high pressure fluid flowing through the turbine stages must pass through a series of stationary and rotary components. Annular, segmented seals mounted on the stationary components are used to control leakage of fluid along the path between the stationary and rotary components. The efficiency of the turbine is directly dependent on the ability of the segmented seals or packing segments to prevent leakage, for example, between the rotor and stator. In certain designs, external springs maintain the packing segments radially outwardly of the rotor, for example, during start-up and shutdown. After the rotor has been brought up to speed, fluid pressure is supplied between the packing segments and a cavity in the rotor casing behind the segments to displace the segments radially inwardly to obtain smaller clearances with the rotor. However, dimensions of smaller industrial turbines prevent installation of retro-fit improved seals without costly and outage extending machining.